1. Field of the Invention
The present invention relates a fluid machinery and more particularly, a fluid pressure apparatus such as fluid compressor, which is especially provided with an improved sliding mechanism.
2. Related Art
With respect to material for forming a sliding mechanism of a fluid machinery such as a compressor or a vacuum pump, there have conventionally been utilized either combination of resin including fluorocarbon resin with metallic material or such metallic material subjected to a hard surface treatment, or combination of the above-mentioned resin with ceramics having a high hardness.
The above-mentioned material combination for the sliding mechanism is significant for performance of the fluid machinery. There have been recognized many cases in which the above-mentioned material combination was applied to a part of a movable sealing unit, which was to be moved in a state contacting a component of the fluid machinery to provide a sealing function.
Such a sliding mechanism or sealing unit has been normally used in a non-lubricant supply type fluid machinery or apparatus to which lubricant oil is not specifically supplied, as shown in Japanese Laid-Open Patent Publication No. H7-247966 and Japanese Laid-Open Patent Publication No. 2000-314383.
In general, it is difficult in actuality to cause the sliding surface of the sliding mechanism to be coincident completely geometrically with a surface of a counterpart at a initial stage of the sliding motion. As a result, the sliding surface of the sliding mechanism repeats the behavior of getting close to the surface of the counterpart, sliding thereon and getting away therefrom, thus causing an extremely complicated motion.
Consequently, in the conventional structure in which a direct sliding motion between the resin member and the metallic member (or something with a hard surface, which has the hardness similar to or larger than metallic member) occurs, the contact surface pressure may increase locally, especially at the initial stage of the compression operation, with the result that the metallic member abrades the resin member, leading to a serious local abrasion of the resin member.
The above-mentioned abrasion in the sliding mechanism leads to much play in the parts and causes a problem of occurrence of abnormal vibration and abnormal noise during operation of the fluid apparatus. In the case of the movable sealing unit, which provides the sealing function, while sliding, even a partial abrasion may lead to leak of fluid, thus failing to achieve the functions. Accordingly, the above-mentioned local abrasion impairs reliability of the fluid machinery provided with such a sealing structure.
With respect to measures to solve the defects or inconveniences mentioned above, there have been measures of (a) converting the shape of the resin-formed member of the sealing unit into a shape, which is flexibly deformable, in order to prevent the contact surface pressure from being increased locally and (b) smoothing the surface of the metallic member into a predetermined surface roughness in order to prevent the resin member from being abraded by the metallic member.
However, the measures (a) makes the structure complicated and degrades degree of freedom in design, thus causing the other problem of deterioration in an assembling operation. On the other hand, the measures (b) cause the other problems of difficulty in working and lack of productivity.
In addition, in a sliding motion between the fluorocarbon resin member and the metallic member, there may occur a phenomenon that even a sufficiently smooth surface may promote abrasion and does not always provide an abrasion prevention effect, thus being inconvenient.
These defects will be described hereunder, taking an example of the sliding motion between the fluorocarbon resin member and the metallic member.
In general, the fluorocarbon resin has the characteristic properties, i.e., a low-friction property and a low-abrasion property in the sliding motion in which no lubricant oil is supplied. Because the fluorocarbon resin has the strongest covalent bond (binding) in constituent atoms in comparison with the other kind of resin, with the result that the fluorocarbon resin is the most chemically stable compound, thus providing a low surface energy, an attractive force relative to the counterpart on the contact surface is small in a microscopic observation, thus leading to a low friction in the sliding motion in a macroscopic observation, and an amount of heat generated by the sliding motion is small, thus eliminating degradation of functions of the sliding mechanism.
However, the actual area contacting the counterpart during the sliding motion increases, according as the surface of the metallic member becomes smoother. Accordingly, an amount of heat generated by friction may increase even in the sliding motion between the fluorocarbon resin member and the metallic member, thus deteriorating the strength of the structural components (i.e., the occurrence of softening and a local fusion in some instances) and resulting in development of abrasion of the fluorocarbon resin member.
Another mechanism indicative of the low abrasion in the sliding motion between the fluorocarbon resin member and the metallic member is that a portion of the fluorocarbon resin migrates onto the surface of the counterpart, i.e., the metallic member so that both the sliding surfaces are formed of fluorocarbon resin in a macroscopic observation, thus forming the stable sliding surfaces and providing a stable abrasion property at low level, as shown in FIGS. 14A and 14B. However, in the case where the metallic member has an excessively large surface roughness, a sufficient amount of abrasion of the fluorocarbon resin, with which the irregularities of the metallic member are filled, causes the occurrence of leak in the sealing structure, thus providing an unfavorable result. In the case where the metallic member has an excessively small surface roughness, there cannot be ensured a function of anchoring the migrated portion of the fluorocarbon resin on the metallic member. More specifically, there cannot be obtained a sufficient contact strength by which the migrated portion of the fluorocarbon resin can be held on the surface of the metallic member. Accordingly, the development of abrasion cannot be avoided. After all, setting the surface roughness of the metallic member to any value makes it impossible to achieve an excellent abrasion property, thus causing problems.